During the drilling, testing, and completion of oil and gas wells numerous downhole tools are used that utilize radially protruding members (blades) that contact the well bore wall to center, position, stabilize, and/or steer the tool in the well bore. For example, in directional drilling applications, which are commonly used to more fully exploit hydrocarbon reservoirs, drill assemblies are typically utilized that include a plurality of independently operable blades to apply force on the well bore wall during drilling to maintain the drill bit along a prescribed path and to alter the drilling direction. Such blades are typically disposed on the outer periphery of the drilling assembly body or on a non-rotating sleeve disposed around a rotating drive shaft. One or more of the blades may be moved in a radial direction, e.g., using electrical or hydraulic devices, to apply force on the well bore wall in order to steer the drill bit outward from the central axis of the well bore.
Prior art downhole tools, such as the Autotrak® steering tool (available from Baker Hughes Incorporated, Houston, Tex.), typically utilize blades that are coupled to the tool body at a hinge. Alternatively, such as in the steering tool disclosed by Webster (U.S. Pat. No. 5,603,386), the blades are not directly coupled to the tool body, but rather to one or more actuators that are in turn mounted on the tool body.
Downhole tools that include blades typically are further capable of retracting the members inward towards the tool body. Such retraction may be required, for example, at the end of an operation, such as a drilling or survey operation, to allow the tool to be withdrawn from the well bore without becoming lodged therein or damaging the blades. One drawback with the above described prior art downhole tools, is that they tend to require complex mechanical and/or pneumatic/hydraulic devices for extending and retracting the blades. Such mechanisms for extending and retracting typically have a number of interoperable moving parts, whose complexity tends to inherently reduce the reliability of the downhole tool. Moreover, such mechanisms are not always suitable for smaller diameter tools.
U.S. Pat. No. 6,761,232 to Moody et al., which is commonly assigned with the present application and is hereinafter referred to as the Moody patent, discloses a downhole steering tool including one or more elastically spring biased blades. The blades each include a moveable end that is free to move relative to the tool body and that may be extended outwards from the tool via an actuation module. Upon de-actuation, the elastically spring biased blades retract. The blades also include a fixed end, which is mechanically connected to or integral with the tool body. While the use of such elastically spring biased blades may be serviceable for some applications, there is room for yet further improvement. For example, such blades may be prone to lateral translation or tilting in response to stress build-up in the blade.
Therefore, there exists a need for downhole steering tools including an improved mechanism for extending and retracting the blades, in particular one that is suitable for small diameter tools. The also exists a need for improved blade controllability and stability for such tools.